What is PI used for?

Answer 1

Pi is used to find a lot of things, volume, area, diameter, radius, but most commonly, circumference. To do that, you multiply the diameter of a circle by pi, (3.14159) then you have the circumference.

it is used to calculate the area and volume of a circle or cylinder

also to find circumference

EX:

DIAMETER X PI = CIRCUMFERENCE

+++

True but I'd question the "most commonly" because Pi is also fundamental to a huge range of calculations involving motion or force in circular or circle-function paths, and to harmonic calculations (sound, vibration, electrical circuit laws, etc.).

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Incidentally, there is a neat trick by pure co-incidence worth knowing if you often use a calculator or the calculator pad on a PC keyboard to find areas of circles from their diameters. The standard formula is Pi*R^2 where R is the circle's radius, but since 2R = Diameter the formula w.r.t Diameter is therefore (Pi*D^2)/4. Now, Pi/4 = 0.7854 to enough decimal places for most everyday calculations, so then the formula simplifies to 0.7854*D^2. Look at your keypad and you see those 4 digits sit in a tidy square in the top left, nice and easy to find if you need to keep entering them!